Monday, November 15, 2010

DCS Advanced Control Concepts

The continuing improvement of programmable logic controller (PLC) has provided very powerful hardware and software tools for obtaining maximum performance from control loops. The main objective of any control loop is to minimize process variability. This is the most important condition to ensure uniform product quality and thus minimize product waste. This can be applied to any industry. Keeping process parameter at their nominal values is the main requirement for any control loop.

In practice, many control loops are tuned by trial and error procedure and thus are operating far from optimal, delivering poor performance. Dead time resulting from transportation of materials and energy is often found in process industries. Processes with large dead time are found to be very hard to control. This is due to the fact that dead time reduces gain and phase margin which can lead to instability. Therefore, gain has to be limited to preserve stability which effectively reduces loop performance. In many cases, a simple PID controller can’t provide the desired loop performance, which means that more advanced control structures must be applied.

Advanced control concepts are typically implemented in Distributed Control System (DCS) and applied in large controlling and complex processes. Most DCS systems have built in functional software structures made for more advanced control designs.


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